Genetic markers for diagnosis of tuberculosis caused by mycobacterium tuberculosis

ABSTRACT

The application is related to novel signature sequences for diagnosis of  Mycobacterium tuberculosis  in clinical samples with 100% specificity and a very high degree of sensitivity.

RELATED APPLICATION

This application is related to and takes priority from the Indian Provisional Application 5572/CHE/2013 filed on Dec. 3, 2013 and is incorporated herein in its entirety.

FIELD OF THE INVENTION

The application is related to novel signature sequences for diagnosis of Mycobacterium tuberculosis in clinical samples. These signature sequences have the ability to differentiate Mycobacterium tuberculosis DNA from other mycobacterial species by PCR with 100% specificity and very high sensitivity.

BACKGROUND OF THE INVENTION

Tuberculosis (TB) is a major global health problem with an alarming rate of mortality associated with it. It is one of the leading infectious diseases caused by bacteria taking one human life every 15-20 seconds globally. Estimates of 2011 reveal that there are almost 9 million new cases and 1.4 million TB deaths (Global Tuberculosis Report 2012, WHO 2013). The disease is caused by Mycobacterium tuberculosis, a member of the genus Mycobacterium, while in a few cases Mycobacterium bovis has been reported to be the causal organism. More than 100 mycobacterium species are known and among them only a few are pathogenic for humans.

Conventional diagnostic methods include examination of sputum smear under a microscope for acid-fast mycobacteria and radiological reading of lungs. However, in most cases the sputum smear examination turns out to be negative for the bacteria due to early stages of infection and lung changes are not readily visible on an x-rays until several months into the infection.

Diagnosis of mycobacteria-related disease poses difficulties for several reasons which have been recognized by researchers and clinicians over the years. Firstly, these bacteria are in small numbers and are already at a contagious stage when they become detectable by conventional methods. Pulmonary disease caused by different mycobacteria are not readily detectable clinically or radiologically. Detection of organism in culture achieves 100% specificity but the growth of mycobacteria in culture takes about 3-6 weeks (Bates et al, Am. Respir. 134, 415-417, 1986) thus making the process time-consuming. In addition, repeated cultures may be required to ensure success.

Several molecular tests for tuberculosis have been developed in the past. These include the Gen-probe ‘Amplified mycobacterium direct test’ by Abbe et al (J. Clin. Mincrobiol. 31, 3270, 1993), ligase chain reaction (LCR) (J. Clin. Microbiol. 35, 2424, 1997), PCR based Roche Amplicor TB test (J. Clin. Microbiol. 33, 1832, 1995) and IS6110 based detection (J. Clin. Microbiol. 28, 2668, 1990).

U.S. Pat. No. 5,168,039 discloses the IS6110 based detection of M. tuberculosis wherein a repetitive DNA segment specific for members of M. tuberculosis complex is used for the diagnosis. While IS6110 based detection system has been shown to have high level of specificity, there are also reports on false positive detections of 3 to 20% making it unreliable (J. Clin. Microbiol. 32, 277, 1994). In addition, lack of IS6110 sequence in some M. tuberculosis strains may also limit the use of the same for diagnostic tests routinely (Tuber. Lung Dis. 76, 550, 1995). U.S. Pat. No. 7,638,309 provides detection of mycobacteria in clinical specimens in the intergenic region between methyl mycotic acid synthase genes mmaA1 and mmaA2 and the flanking region in mmaA1 and mmaA2 genes.

Thus, it appears that there is a paucity of simple, rapid and reliable tests that can specifically detect M. tuberculosis during early stages of the disease. The present invention has identified ‘signature sequences’ that can differentiate M. tuberculosis from a large number of other mycobacterial DNA. These ‘signature sequences’ are used in detection of early disease in clinical samples of patients.

SUMMARY OF THE INVENTION

The invention provides novel signature sequences for diagnosis of Mycobacterium species (sps) in clinical samples with 100% specificity and a very high degree of sensitivity.

In one aspect, the invention provides a nucleotide sequence capable of selectively detecting pathogenic Mycobacterium sps using oligonucleotide primers corresponding to the signature sequence selected from SEQ ID NO: 1, 2, 3 or 4.

In another aspect the invention provides a method of detecting pathogenic mycobacterium sps in a clinical sample, said method comprising the steps of:

a. removal of contaminants from the clinical sample by conventional methods;

b. extraction of genomic DNA from the contaminant-free clinical sample;

c. designing a set of specific oligonucleotide primers capable of specifically detecting SEQ ID NO: 1, 2, 3 or 4 for use in RT-PCR;

d. analyzing PCR product by electrophoresis or specific probe nucleotide sequence complementary to SEQ ID NO: 1, 2, 3 or 4.

The set of oligonucleotide primers of the invention are selected from

(i)    5′ ATGCAGGTTGCGACTGTACACCCGG 3′        3′ GGCCGCTCTTGTTCTTCGTCGGAT 5′ (ii)   5′ GTGTTTGCGTTGAGTAATAATCTGAACCGTGT 3′        3′ AGCCAATTCCAGCACGATGTCGCC 5′ (iii)  5′ ATGCAGGTTGCGACTGTACACCCGG 3′        3′ GGCCGCTCTTGTTCTTCGTCGGAT 5′ (iv)   5′ TGTACCGCGTGCCCGACGATTTG 3′        3′ ACAGGCAGCTAACAGGGCGTCGG 5′

(v) a set of oligonucleotide primers complementary to (i), (ii), (iii) or (iv) or

(vi) a set of oligonucleotide primers comprising of sequence containing any 10 consecutive bases from one of the sequences selected from SEQ ID NO: 1, 2, 3 or 4.

In yet another aspect, the invention provides a kit for the detection of pathogenic mycobacterium sps in clinical samples, said kit comprising set of oligonucleotide primers selected from

(i)    5′ ATGCAGGTTGCGACTGTACACCCGG 3′        3′ GGCCGCTCTTGTTCTTCGTCGGAT 5′ (ii)   5′ GTGTTTGCGTTGAGTAATAATCTGAACCGTGT 3′        3′ AGCCAATTCCAGCACGATGTCGCC 5′ (iii)  5′ ATGCAGGTTGCGACTGTACACCCGG 3′        3′ GGCCGCTCTTGTTCTTCGTCGGAT 5′ (iv)   5′ TGTACCGCGTGCCCGACGATTTG 3′        3′ ACAGGCAGCTAACAGGGCGTCGG 5′

(v) a set of oligonucleotide primers complementary to (i), (ii), (iii) or (iv) or

(vi) a set of oligonucleotide primers comprising of sequence containing any 10 consecutive bases from one of the sequences selected from SEQ ID NO: 1, 2, 3 or 4.

Furthermore, the invention provides a method of detecting pathogenic mycobacterium sps in a clinical sample wherein the sample is isolated from individuals vaccinated against tuberculosis. It also provides a method of detecting pathogenic mycobacterium sps in a clinical sample wherein the sample is isolated from individuals treated against tuberculosis.

BRIEF DESCRIPTION OF FIGURES

FIG. 1A: Amplification of SS1 at low and varied DNA template concentrations.

FIG. 1B: Amplification of SS2 at low and varied DNA template concentrations.

FIG. 1C: Amplification of SS3 at low and varied DNA template concentrations.

FIG. 1D: Amplification of SS4 at low and varied DNA template concentrations.

FIG. 2: Amplification of signature sequences SS1, SS2, SS3 and SS4 from patient sputum samples.

FIG. 3: Amplification of signature sequences SS1 and SS3 from patient blood samples.

DETAILS OF THE INVENTION

The present invention relates to detection of pathogenic Mycobacterium species using signature sequences SEQ ID NO: 1, 2, 3 or 4 with a high degree of sensitivity and 100% specificity.

In one embodiment, the invention provides novel DNA diagnostic markers for specific detection of Mycobacterium tuberculosis which causes tuberculosis.

A three-pronged approach was carried out to identify novel DNA diagnostic marker for detection of pathogenic mycobacterium sps, especially, Mycobacterium tuberculosis. First step provides an in-silico approach to identify and shortlist potential sequences of Mycobacterium, unique and exclusive to pathogenic mycobacterium sps, especially Mycobacterium tuberculosis. The criteria used for selection of the potential sequences are presented below which involves comparative proteomic analysis of 13 mycobacterium species:

-   -   i. Strict pathogens (the most virulent pathogens) such as         Mycobacterium tuberculosis, Mycobacterium laprae, Mycobacterium         ulcerous and Mycobacterium bovis.     -   ii. Opportunistic pathogens, which belong to Non Tuberculous         Mycobacteria (NTM) group, can cause pulmonary and other         disseminated infections in immune compromised individuals         (Infect. Genet. Evol. 12, 832, 2012; Appl. Environ. Microbiol.         79, 825, 2013). Mycobacterium marinum, Mycobacterium avium,         Mycobacterium intracellulare, Mycobacterium aviumpara         tuberculosis and Mycobacterium abscessus, cause opportunistic         pulmonary infection in human whereas Mycobacterium avium         subspecies paratuberculosis (MAP), the third member of MAC is         the suspected causative agent of Crohn's disease in human (Appl.         Environ. Microbiol. 79, 825, 2013; Crit. Rev. Microbiol. 38, 52,         2012).     -   iii. Non-pathogenic group includes Mycobacterium gilvum,         Mycobacterium vanbaalenii, Mycobacterium smegmatis and         Mycobacterium indicus pranii, which does not cause disseminated         infections even in immune compromised individuals (BMC         Microbiol. 10, 237, 2010; Infect. Genet. Evol., 12, 853, 2012;         Br. J. Exp. Pathol. 52, 627, 1971).

The following bioinformatics process flow resulted in the identification of potential gene markers of the invention.

-   -   a) Perform all against all NCBI BLAST (J Mol Biol., 215,         403, 1990) on the protein sequences from the selected genomes.     -   b) Perform all against all NCBI BLAST ((J Mol Biol., 215,         403, 1990) on the nucleotide sequences from the selected         genomes.     -   C) Identify Protein Domains from Pfam (Comp. Genomics, 396,         43, 2007) and GENE-3D/CATH (Nucleic Acids Research, 40,         D465, 2012) using InterPro (Nucleic Acids Research, 40, D306,         2012).     -   d) Classify sequences into three categories namely i) CLASS 1         and ii) CLASS 2 as potential hits and iii) rest as non-hits.

The above process flow resulted in the classification of the potential hits into class 1 and class 2. As per the present invention, class 1 are genes unique to the organism of interest based on the fact that they do not share protein domain and protein sequence identity of more than 20% and nucleotide sequence identity of more than 35% with any other organism in the selected organism list. In another embodiment, class 2 genes are those that do not share protein domain and protein sequence identity of more than 20% and nucleotide sequence identity of more than 35% with any other organism in the selected organism list.

Table 1 provides potential candidate genes carrying ‘signature sequences’ based on the bioinformatics process flow.

TABLE 1 Potential “signature sequences” carrying candidate genes H37Rv Gene Identifiers Class H37Rv protein description Rv1507A 1 Hypothetical protein Rv1509 1 Hypothetical protein Rv2645 1 Hypothetical protein Rv2653c 1 Possible PhiRv2 prophage protein Rv2654c 1 Possible PhiRv2 prophage protein Rv2658c 1 Possible prophage protein Rv0064A 2 Possible antitoxin VapB1 Rv0078B 2 Hypothetical protein Rv0397A 2 Hypothetical protein Rv0456B 2 Possible antitoxin MazE1 Rv0959A 2 Possible antitoxin VapB9 Rv1366A 2 Hypothetical protein Rv1954A 2 Hypothetical protein Rv1991A 2 Antitoxin MazE6 Rv2142A 2 Possible antitoxin ParD2 Rv2231A 2 Possible toxin VapC16 Rv2231B 2 Possible antitoxin VapB16 Rv2274A 2 Possible antitoxin MazE8 Rv2395A 2 Acid and phagosome regulated protein A AprA Rv2395B 2 Acid and phagosome regulated protein B AprB Rv2862A 2 Possible antitoxin VapB23 Rv3190A 2 Hypothetical protein Rv3344c 2 PE-PGRS family protein PE_PGRS49] [partial = 5′] Rv3512 2 PE-PGRS family protein PE_PGRS56] [partial = 5′] Rv3599c 2 Hypothetical short protein

In one aspect, the invention functionally characterizes the potential ‘signature sequences (SS)’-carrying candidate genes based on functional information retrieved from Tuberculist (Tuberculosis (Edinb) 91, 7, 2011) and TB database (Nucleic Acids Research, 37, D499, 2009). Accordingly, the potential signature sequences can be functionally characterized into the following groups:

-   -   a. 9 (Rv0064A, Rv0456B, Rv0959A, Rv1991A, Rv2142A, Rv2231A,         Rv2231B, Rv2274A and Rv2862A) fell into the toxin-antitoxin         category.     -   b. 3 (Rv2653c, Rv2654c, Rv2658c) are possible prophages.     -   c. 2 (Rv3344c and Rv3512) belong to PE_PGRS family of proteins     -   d. 2 (Rv2645 and Rv2653c) are deleted (partially or completely)         in one or more clinical isolates eliminating their use as         diagnostic markers.     -   e. 9 (Rv1507A, Rv1509, Rv0078B, Rv2645, Rv0397A, Rv1366A,         Rv1954A, Rv3599c, Rv3190A) are hypothetical proteins.     -   f. 2 (Rv2395A, Rv2395B) are acid and phagosome regulated         proteins.

Based on the in-silico analysis, two Class 1 genes (Rv1507A and Rv1509) and two Class 2 genes (Rv1954A and Rv2231A) with homologs in Mycobacterium bovis BCG were selected as potential candidates (Table 2).

TABLE 2 Nucleotide Sequences of Potential “signature sequences” carrying genes Prediction Gene Name Sequence Description Class Rv1507A >Rv1507A Gene length: CLASS 1 hypothetical ATGCAATCAGGTCAAAATATCCTCGCCAAGG 504 bp, protein TATGTAATTTGATTGAACAATCGCGACTTTC Protein length: TTCAACGCGGTGTCTCCAATTTAGAATAACA 167 aa AATACGTCGCGCCCGCGACAGCTCCGCTGGA GCGAGTTCAAGCGATTCTGCGACATATTCAA TATGGTGCTCGGGAAGGCCAGGATGGGCCGC GACCCGGGGCGTCCGGTGCGCGATGAACGTC GCATCGTCTCCTGTGAGATAATTGCATCCGA TCATATAGGGCTGGCTGCGGCTAGGTTGCTG GCAAAAAGATATCGCGGCCGATCCGTTTCTG GTTTTGTCTTGATGATCAAATCCGCTTCCGT TCACGAGATCGATTCCTGGTCTTCCCCCAGC GTCGCGATGTCGATAGGTGTCGCGCTTTGTT CGTACCCGCACTACGCGGCGGCGAGAACCTC GCCACCGAATCGGGATTGGGGGGAGGATACC ACTCGGTCGAGGCCCGTCACCGGCCTTCTAG CGGGTTG Rv1509 >Rv1509 Gene length: CLASS 1 Essential GTGTTTGCGTTGAGTAATAATCTGAACCGTG 882 bp, hypothetical TGAACGCATGCATGGATGGATTCCTTGCCCG Protein length: protein TATCCGCTCACATGTTGATGCGCACGCGCCA 293 aa GAATTGCGTTCACTGTTCGATACGATGGCGG CCGAGGCCCGATTTGCACGCGACTGGCTGTC CGAGGACCTCGCGCGGTTGCCTGTCGGTGCA GCATTGCTGGAAGTGGGCGGGGGGGTACTTC TGCTCAGCTGTCAACTGGCGGCGGAGGGATT TGACATCACCGCCATCGAGCCGACGGGTGAA GGTTTTGGCAAGTTCAGACAGCTTGGCGACA TCGTGCTGGAATTGGCTGCAGCACGACCCAC CATCGCGCCATGCAAGGCGGAAGACTTTATT TCCGAGAAGCGGTTCGACTTCGCCTTCTCGC TGAATGTGATGGAGCACATCGACCTTCCGGA TGAGGCAGTCAGGCGGGTATCGGAAGTGCTG AAACCGGGGGCCAGTTACCACTTCCTGTGCC CGAATTACGTATTCCCGTACGAACCGCATTT CAATATCCCAACATTCTTCACCAAAGAGCTG ACATGCCGGGTGATGCGACATCGCATCGAGG GCAATACGGGCATGGATGACCCGAAGGGAGT CTGGCGTTCGCTCAACTGGATTACGGTTCCC AAGGTGAAACGCTTTGCGGCGAAGGATGCGA CGCTGACCTTGCGCTTCCACCGTGCAATGTT GGTATGGATGCTGGAACGCGCGCTGACGGAT AAGGAATTCGCTGGTCGCCGGGCACAATGGA TGGTCGCTGCTATTCGCTCGGCGGTGAAATT GCGTGTGCATCATCTGGCAGGCTATGTTCCC GCTACGCTGCAGCCCATCATGGATGTGCGGC TAACGAAGAGGTAA Rv1954a >gi|448814763:2201231-2201623 Gene length: CLASS 2 Hypothetical Mycobacterium tuberculosis H37Rv 303 bp, protein complete genome Protein length: TGGTATAAGCTGGTTTTAGACGAAAAGGACC 100 bp CCACCTCGGGGTCTGATGGCCAGGGGCAGGG TCGTGTGCATTGGGGATGCAGGTTGCGACTG TACACCCGGCGTGTTCCGCGCGACAGCGGGT GGGATGCCGGTGCTGGTGGTCATCGAGTCTG GGACAGGAGGTGATCAGATGGCTCGTAAAGC TACGTCCCCGGGTAAGCCGGCTCCGACGTCG GGACAGTATCGCCCGGTTGGCGGTGGCAACG AGGTGACCGTTCCGAAGGGACACCGTCTGCC TCCCTCGCCCAAGCCCGGTCAGAAGTGGGTG AACGTCGATCCGACGAAGAACAAGAGCGGCC GCGGCTGAGCTTGTGCCGTCGGGATGGGTGT CGCACCGTCTCGGCGGGTCGC Rv2231A >gi|448814763:c2506224-2505671 Gene length: CLASS 2 Mycobacterium tuberculosis H37Rv 426 bp, complete genome Protein length: GCCGCGGCGAGCCGGTAGCAAAGCTTGTGCC 141 aa GCTGCATCCTCATGAGACTCGGCGGTTAGGC ATTGACCATGGCGTGTACCGCGTGCCCGACG ATTTGGACGCTCCGTTGTCAGACGACGTGCT CGAACGCTTTCACCGGTGAAGCGCTACCTCA TCGACACCCACGTTTGGCTGCGGATGCCGTC AACGAAACACGGGCGATTGTTCAGGACGTCC GCAACAGCATTCTCTTGTCGGCCGCCAGTGC CTGGGAGATCGCGATCAACTACCGCCTCGGC AAGCTCCCGCCGCCCGAGCCATCGGCCTCTT ACGTGCCCGATCGAATGCGCCGCTGCGGCAC GTCGCCGCTGTCAGTTGACCACGCACACACT GCGCACCGCAGAGCTTCCGGATCACCATCGA CATCCATTCGACCGTGTGCTCATCGCCCAGG CACAGCTGCTTGGCCTGACGATCATCACCGC CGACGCCCTGTTAGCTGCCTGTGATGTCGCG GTTGTCGCCGCGTAGACAACGCGTCGGCGGT GCTCTGGATTCTTGGCCCGCACACCG

In a most preferred aspect, the signature sequences were designed keeping in view the diagnostic tool of RT PCR. These were short sequences amenable for PCR amplification from selected genes. The specific signature sequences, SS1 (Rv1507A), SS2 (Rv1509), SS3 (RV1954A) and SS4 (Rv2231A) of the invention are provided below. Homology search using NCBI nucleotide BLAST against the genus Mycobacterium was conducted on these signature sequences to confirm their uniqueness.

SS1 (Rv1507A): >Rv1507A SEQ ID NO: 1 ATGCAATCAGGTCAAAATATCCTCGCCAAGGTATGTAATTTGATTGAACA ATCGCGACTTTCTTCAACGCGGTGTCTCCAATTTAGAATAACAAATACGT CGCGCCCGCGACAGCTCCGCTGGAGCGAGTTCAAGCGATTCTGCGACATA TTCAATATGGTGCTCGGGAAGGCCAGGATGGGCCGCGACCCGGGGCGTCC GGTGCGCGATGAACGTCGCATCGTCTCCTG SS2 (Rv1509): >gi|448814763:1700212-1701093 Mycobacterium tuberculosis H37Rv complete genome SEQ ID NO: 2 GTGTTTGCGTTGAGTAATAATCTGAACCGTGTGAACGCATGCATGGATGG ATTCCTTGCCCGTATCCGCTCACATGTTGATGCGCACGCGCCAGAATTGC GTTCACTGTTCGATACGATGGCGGCCGAGGCCCGATTTGCACGCGACTGG CTGTCCGAGGACCTCGCGCGGTTGCCTGTCGGTGCAGCATTGCTGGAAGT GGGCGGGGGGGTACTTCTGCTCAGCTGTCAACTGGCGGCGGAGGGATTTG ACATCACCGCCATCGAGCCGACGGGTGAAGGTTTTGGCAAGTTCAGACAG CTTGGCGACATCGTGCTGGAATTGGCTGCA SS3 (RV1954A): >gi|448814763:2201277-2201579 Mycobacterium tuberculosis H37Rv complete genome SEQ ID NO: 3 ATGGCCAGGGGCAGGGTCGTGTGCATTGGGGATGCAGGTTGCGACTGTAC ACCCGGCGTGTTCCGCGCGACAGCGGGTGGGATGCCGGTGCTGGTGGTCA TCGAGTCTGGGACAGGAGGTGATCAGATGGCTCGTAAAGCTACGTCCCCG GGTAAGCCGGCTCCGACGTCGGGACAGTATCGCCCGGTTGGCGGTGGCAA CGAGGTGACCGTTCCGAAGGGACACCGTCTGCCTCCCTCGCCCAAGCCCG GTCAGAAGTGGGTGAACGTCGATCCGACGA SS4 (Rv2231A): >gi|448814763:c2506161-2505736 Mycobacterium tuberculosis H37Rv complete genome SEQ ID NO: 4 TTGACCATGGCGTGTACCGCGTGCCCGACGATTTGGACGCTCCGTTGTCA GACGACGTGCTCGAACGCTTTCACCGGTGAAGCGCTACCTCATCGACACC CACGTTTGGCTGCGGATGCCGTCAACGAAACACGGGCGATTGTTCAGGAC GTCCGCAACAGCATTCTCTTGTCGGCCGCCAGTGCCTGGGAGATCGCGAT CAACTACCGCCTCGGCAAGCTCCCGCCGCCCGAGCCATCGGCCTCTTACG TGCCCGATCGAATGCGCCGCTGCGGCACGTCGCCGCTGTCAGTTGACCAC GCACACACTGCGCACCGCAGAGCTTCCGGATCACCATCGACATCCATTCG ACCGTGTGCTCATCGCCCAGGCACAGCTGCTTGGCCTGA

For the purposes of PCR validation, the signature sequences SS1, SS2, SS3 and SS4 were selected and oligonucleotide primers were designed to generate corresponding specific PCR amplification products. Table 3 provides the set of designed oligonucleotide primers.

TABLE 3 Signature sequences SS1, SS2, SS3 and  SS4 and respective oligonucleotide primers Signature Sequences Prediction (SS) Sequence Description Class SS1 from >Rv1507A NZE_Rv1954A_F CLASS 1 Rv1507A ATGCAATCAGGTCAAAATATCCTCGCC ATGCAGGTTGCGA AAGGTATGTAATTTGATTGAACAATCG CTGTACACCCGG CGACTTTCTTCAACGCGGTGTCTCCAA Length = 25,  TTTAGAATAACAAATACGTCGCGCCCG Tm = 58.6, CGACAGCTCCGCTGGAGCGAGTTCAAG % G + C = 60 CGATTCTGCGACATATTCAATATGGTG NZE_Rv1954A_R CTCGGGAAGGCCAGGATGGGCCGCGAC GGCCGCTCTTGTT CCGGGGCGTCCGGTGCGCGATGAACGT CTTCGTCGGAT CGCATCGTCTCCTG Length = 24,  Tm = 57.4, % G + C = 58.3 Amplicon  Size = ~280 bp SS2 from >gi|448814763:1700212-1701093 NZE_Rv1509_F CLASS 1 Rv1509 Mycobacterium tuberculosis H37Rv GTGTTTGCGTTGA complete genome GTAATAATCTGAA GTGTTTGCGTTGAGTAATAATCTGAAC CCGTGT CGTGTGAACGCATGCATGGATGGATTC Length = 32,  CTTGCCCGTATCCGCTCACATGTTGAT Tm = 57.5 GCGCACGCGCCAGAATTGCGTTCACTG % G + C = 41 TTCGATACGATGGCGGCCGAGGCCCGA NZE_Rv1509_R TTTGCACGCGACTGGCTGTCCGAGGAC AGCCAATTCCAGC CTCGCGCGGTTGCCTGTCGGTGCAGCA ACGATGTCGCC TTGCTGGAAGTGGGCGGGGGGGTACTT Length = 24,  CTGCTCAGCTGTCAACTGGCGGCGGAG Tm = 58.8, GGATTTGACATCACCGCCATCGAGCCG % G + C = 58.3 ACGGGTGAAGGTTTTGGCAAGTTCAGA Amplicon  CAGCTTGGCGACATCGTGCTGGAATTG Size = ~330 bp GCTGCA SS3 from >gi|448814763:2201277-2201579 NZE_Rv1954A_F CLASS 2 Rv1954A Mycobacterium tuberculosis H37Rv ATGCAGGTTGCGA complete genome CTGTACACCCGG ATGGCCAGGGGCAGGGTCGTGTGCATT Length = 25,  GGGGATGCAGGTTGCGACTGTACACCC Tm = 58.6, GGCGTGTTCCGCGCGACAGCGGGTGGG % G + C = 60 ATGCCGGTGCTGGTGGTCATCGAGTCT NZE_Rv1954A_R GGGACAGGAGGTGATCAGATGGCTCGT GGCCGCTCTTGTT AAAGCTACGTCCCCGGGTAAGCCGGCT CTTCGTCGGAT CCGACGTCGGGACAGTATCGCCCGGTT Length = 24,  GGCGGTGGCAACGAGGTGACCGTTCCG Tm = 57.4, AAGGGACACCGTCTGCCTCCCTCGCCC % G + C = 58.3 AAGCCCGGTCAGAAGTGGGTGAACGTC Amplicon  GATCCGACGA Size = ~280 bp SS4 from >gi|448814763:c2506161-2505736 NZE_Rv2231A_F CLASS 2 Rv2231A Mycobacterium tuberculosis H37Rv TGTACCGCGTGCC complete genome CGACGATTTG TTGACCATGGCGTGTACCGCGTGCCCG Length = 23,  ACGATTTGGACGCTCCGTTGTCAGACG Tm = 59.1, ACGTGCTCGAACGCTTTCACCGGTGAA % G + C = 61 GCGCTACCTCATCGACACCCACGTTTG NZE_Rv2231A_R GCTGCGGATGCCGTCAACGAAACACGG ACAGGCAGCTAAC GCGATTGTTCAGGACGTCCGCAACAGC AGGGCGTCGG ATTCTCTTGTCGGCCGCCAGTGCCTGG Length = 23,  GAGATCGCGATCAACTACCGCCTCGGC Tm = 57.1, AAGCTCCCGCCGCCCGAGCCATCGGCC % G + C = 65 TCTTACGTGCCCGATCGAATGCGCCGC Amplicon  TGCGGCACGTCGCCGCTGTCAGTTGAC Size = ~390 bp CACGCACACACTGCGCACCGCAGAGCT TCCGGATCACCATCGACATCCATTCGA CCGTGTGCTCATCGCCCAGGCACAGCT GCTTGGCCTGAC

In a preferred embodiment, pathogenic mycobacterium sps can be detected with 100% specificity following PCR using DNA isolated from clinical samples from patients who presented with clinical symptoms of the disease. In another embodiment, pathogenic mycobacterium sps is also detected using the above method in clinical samples isolated from individuals vaccinated against tuberculosis. In yet another embodiment, pathogenic mycobacterium sps is also detected using the above method in clinical samples isolated from individuals treated against tuberculosis.

Pathogenic mycobacterium sps, as provided in the invention, includes Mycobacterium tuberculosis and Mycobacterium bovis. More specifically, pathogenic mycobacterium sps represents Mycobacterium tuberculosis, the TB causing bacterium.

Clinical samples, as meant here, includes specimens such as blood, sputum, cerebrospinal fluid, gastric lavage, tissue biopsies and the likes thereof. PCR product can be easily visualized by any conventional method that can be readily recognized by a person skilled in the art such as electrophoresis.

Following Examples serve as a tool to illustrate the invention. However, it should in no way be considered to be limiting the invention.

Example 1 Determination of Specificity and Sensitivity of Signature Sequences Genomic DNA for PCR Amplification

Genomic DNA of Mycobacterium tuberculosis and 13 other mycobacterial species were used for testing the specificity of signature sequences using PCR. These include, M. avium subspecies paratuberculosis, M. smegmatis (ATCC19420), M. vaccae, M. marinum (ATCC927), M. chelonae (ATCC14472), M. flavescens (ATCC14474), M. fortuitum (ATCC6481), M. kansasii (ATCC12478), M. bovis (ATCC27294), M. bovis (BCG), M. avium (ATCC25291), M. gastri, M. indicuspranii.

PCR Reaction

The PCR reaction mixture (50 μl) consisted of 10×taqPCR buffer, 0.5 mmolMgCl2, 0.4 mmol dNTP, 10 pmol forward and reverse primers respectively, 4% DMSO and 1Utaq DNA polymerase. The reaction conditions were the following: 95° C. for 5 minutes, followed by 35 cycles of 95° C. for 30 seconds, annealing temperature 50° C. for 30 seconds, 72° C. for 1 minute and finally 72° C. for 10 minutes. All PCR products were electrophoresed on 2% agarose gel with ethidium bromide staining.

The “signature sequences” were tested for their ability to differentiate Mycobacterium tuberculosis DNA from a large number of other mycobacterial DNA in PCR using primers complementary to these “signature sequences” as shown in Table 3. For this purpose, chromosomal DNA extracted from 13 mycobacterium species including human genomic DNA were tested by mycobacterium genus-specific primers of the ‘signature sequences’. SS1 and SS2 were negative for all 13 mycobacterium species tested whereas SS3 and SS4 show positive PCR results only when M. bovis BCG genomic DNA was used as template.

Table 4 summarizes the specificity data resulting from PCR using specific primers of signature sequences SS1, SS2, SS3 and SS4.

TABLE 4 Specific amplification of signature sequences from Mycobacterium tuberculosis and M. bovis BCG Specimen SS1 SS2 SS3 SS4 M. tuberculosis + + + + M. bovis BCG − − − − M. avium − − − − M. smegmatis − − − − M. vaccae − − − − M. avium − − − − M. chelonae − − − − M. flori − − − − M. fortuitum − − − − M. kansasi − − − − M. bovis − − − − M. marinum − − − − M. gastri − − − − MIP − − − − MAP − − − − M. leprae Human Genome − − − −

Furthermore, sensitivity analysis revealed that the signature sequences were highly sensitive in being able to detect <1 ng (100pg) DNA as shown in FIGS. 1A, 1B, 1C and 1D for the four primers of the signature sequences SS1, SS2, SS3 and SS4 respectively.

Example 2

Evaluation of Mycobacterium tuberculosis-Specific Primer Pair Using Clinical Samples A) Amplification of Signature Sequences from Patient Sputum Samples

Sputum samples were processed by the Universal Sample Processing (USP) method for DNA extraction as described by Chakravorty et al (J Clin Microbiol 43, 4357, 2005). DNA was isolated from the USP sediments by boiling in the presence of five volumes of solution containing 10% Chelex-100 resin, 0.03% triton X-100, and 0.3% Tween 20. The isolated DNA was stored at 20° C. and used for PCR assay.

PCR reaction was carried out using specific primers as given in Table 3.

The results show amplification of signature sequences in patient sputum sample (FIG. 2) demonstrating the diagnostic utility of the signature sequences for detecting pathogenic Mycobacterium tuberculosis.

B) Amplification of Signature Sequences from Patient Blood Samples

DNA from blood samples of tuberculosis patients were isolated as per the protocol described in van Heiden et al (isolation of DNA from Mycobacterium tuberculosis, Paul D. van Heiden, Thomas C. Victor, Robin M. Warren, and Eileen G. van Holden)

The results show amplification of SS1 and SS3 as seen in FIG. 3. 

1: A method of detecting Mycobacterium tuberculosis in a clinical sample, said method comprising the steps of: a) removal of contaminants from the clinical sample to generate a contaminant-free clinical sample; b) extraction of genomic DNA from the contaminant-free clinical sample; c) designing a set of specific oligonucleotide primers capable of specifically detecting SEQ ID NO: 2 for use in RT-PCR; d) performing PCR with the oligonucleotide primers of step c) on the genomic DNA of step b) to produce a PCR product; and e) analyzing the PCR product obtained in step d) by electrophoresis or a specific probe nucleotide sequence complementary to SEQ ID NO:
 2. 2: The method of claim 1, wherein the set of oligonucleotide primers are selected from: (i)  (SEQ ID NO: 7) 5′ GTGTTTGCGTTGAGTAATAATCTGAACCGTGT 3′ and (SEQ ID NO: 8) 3′ AGCCAATTCCAGCACGATGTCGCC 5′;

(ii) a set of oligonucleotide primers complementary to (i); or (iii) a set of oligonucleotide primers comprising a sequence containing any 10 consecutive bases from the sequence of SEQ ID NO:
 2. 3: The method of claim 1, wherein the clinical sample is isolated from individuals vaccinated against tuberculosis. 4: The method of claim 1, wherein the clinical sample is isolated from individuals treated against tuberculosis. 